The present invention is directed to electronic devices that can operate in a low power mode to reduce power consumption and, more particularly, to circuitry for buffering power mode control signals.
Integrated circuit (IC) devices, such as data processing systems, often include power control modules that cause selected functional blocks to operate in a low power mode with power supply reduced or cut-off and subsequently to be restored to a full power mode, while leaving other functional blocks supplied continuously with power. A power control module typically includes one or more power gates, which can switch off connection of part or all of the selected blocks to a supply voltage (header gate) or to ground (footer gate). The power gates may be in the power distribution network or in the functional blocks.
The functional blocks whose power is controlled may receive power mode control signals. These power controlled functional blocks may include state-sensitive elements such as state retention cells for saving the data in the blocks before they enter low power mode, and isolation cells for preventing short circuits appearing between the block in low power mode and blocks that are still powered and running. A power mode control signal may be provided by system software and/or hardware and may be generated by a power management controller. The power mode control signal is then distributed to multiple functional blocks by a power mode control distribution network, which typically has serially connected chains of buffers controlling respective blocks. Typically, the serially connected chains of buffers form part of a branching tree, each branch starting from a common input end and distributing the power mode control signals to an output end that is connected to a respective functional block.
It is necessary for the power mode control distribution network to maintain the validity of the distributed power mode control signals whether or not the blocks they control are in low power mode. If the power mode control distribution network is always supplied with power, the leakage current of the network is a significant factor in the standby or sleep current of the IC, which it is desirable to reduce.